Original bug ID: 6814
Reporter: ggole
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2016-12-07T10:49:12Z)
Resolution: not a bug
Priority: normal
Severity: major
Version: 4.02.1
Target version: 4.02.2+dev / +rc1
Fixed in version: 4.02.2+dev / +rc1
Category: typing
Monitored by: @hcarty

Bug description

Compiling the following program with -rectypes results in an assertion failure:

Fatal error: exception File "typing/typecore.ml", line 1899, characters 65-71: Assertion failed

As the comment suggests, replacing the underscore (or compiling without -rectypes) avoids the crash.

type (_, _) t =
| Nil : ('t, 't) t
| Cons : ('t -> 'a) * ('r, 't) t -> (('a -> 'r), 't) t

(* replacing the _ here with b results in no crash *)
let test : type a b . a -> (_, a) t -> unit =
fun value -> function
| Nil -> ()
| Cons (getter, rest) -> ignore (getter value)

I also reproduced on 4.03.0.